Heat storage



FIG. 1 is a front view of the claimed design.

FIG. 2 is a rear view of the claimed design.

FIG. 3 is a left view of the claimed design.

FIG. 4 is a right view of the claimed design.

FIG. 5 is a top view of the claimed design.

FIG. 6 is a bottom view of the claimed design; and,

FIG. 7 is a perspective view of the claimed design.

The broken lines are included for the purpose of illustrating portions of the heat storage that form no part of the claimed design. 

CLAIM I claim the ornamental design for heat storage, as shown and described. 